The present invention relates to a human STAT3 allelic variant, the cDNA sequence encoding it, its use in therapy and/or in diagnosis of autoimmune and/or inflammatory diseases, as well as pharmaceutical compositions comprising it.
Signal Transducer and Activator of Transcription (STAT) proteins are a new class of intracellular transcription factors which play an essential function in the cellular responses to cytokines (Stahl et at., 1994; Gouilleux et at., 1995; Azam et al., 1995; Tian et at., 1994; May et al., 1996; and Iwatsuki et al., 1997).
Most of these proteins have been well characterized by sequencing, and their structure as well as the mechanism of their actions has been extensively analyzed and well documented (Wegenka et al., 1993; Akira et al., 1994; Wegenka et al., 1994; Quelle et al., 1995 and Silva et al., 1996).
These proteins contain SH2 and SH3 domains as well as a phosphorylation site at their carboxy-terminal region (Kapetein et al., 1996; and Herman et al., 1996). After cytokine receptor activation through ligand binding, the intracellular portion of the receptor becomes phosphorylated by an associated kinase of the JAK family. STAT proteins then bind to the phosphorylated receptor, through their SH2 domain, and are in turn phosphorylated by JAKs (Stahl et al., 1995). Phosphorylated STAT proteins then dimerize and translocate to the nucleus, where they are able to recognize specific DNA responsive elements (Seidel et al., 1995; and Harroch et al., 1994).
STAT3 has been identified as an important mediator of the signal imparted by the IL-6 family of cytokines, as well as by EGF and by a number of other interleukins and growth factors.
STAT3 has been shown to play a central role in the upregulation of hepatic acute-phase proteins (Wegenka et al., 1993; and Zhang et al., 1996) in the growth arrest of monocytic cells (Yamanaka et al., 1996; and Minami et al., 1996) as well as in the survival of myeloma cells (Harroch et al., 1994).
During experiments on the analysis of STAT3 interactions, we have amplified by RT-PCR from HepG2 cells a cDNA fragment corresponding to the SH2 domain of human STAT3. We have found by DNA sequencing that the SH2 domain we have isolated shows a divergence of 13 residues over the corresponding sequence of the original published human STAT3 gene (Akira et al., 1994).
In order to determine the nature of this sequence variant, we have designed three pairs of primers with 3xe2x80x2 ends corresponding to nucleotide positions at variance between the two human cDNA sequences.
Upon such investigations it resulted that the new variant corresponds to at least the most frequent allele of human STAT3.
Therefore, the main object of this invention is the above-mentioned allelic variant of human STAT3 protein. In particular, the object of the invention is a polypeptide comprising the amino acid sequence of SEQ ID NO:2, or a functionally equivalent salt, or a functionally equivalent derivative, or an active fraction, or a fusion protein.
The definition xe2x80x9csaltxe2x80x9d as used herein refers both to salts of the carboxyl-groups and to the salts of the amino functions of the compound obtainable through known methods. The salts of the carboxyl-groups comprise inorganic salts as, for example, sodium, potassium, calcium salts and salts with organic bases as those formed with an amine as triethanolamine, arginine or lisine. The salts of the amino groups comprise for example salts with inorganic acids as hydrochloric acid and with organic acids as acetic acid.
The definition xe2x80x9cderivativexe2x80x9d as herein used refers to derivatives which can be prepared from the functional groups present on the lateral chains of the amino acid moieties or on the terminal N- or C-groups according to known methods and are comprised in the invention when they are pharmaceutically acceptable i.e. when they do not destroy the protein activity or do not impart toxicity to the pharmaceutical compositions containing them. Such derivatives include for example esters or aliphatic amides of the carboxyl-groups and N-acyl derivatives of free amino groups or O-acyl derivatives of free hydroxyl-groups and are formed with acyl-groups as for example alcanoyl- or aroyl-groups.
As xe2x80x9cactive fractionxe2x80x9d of the protein the present invention refers to any fragment or precursor of the polypeptidic chain of the compound itself, alone or in combination with related molecules or residues bound to it, for example residues of sugars or phosphates, or aggregates of the polypeptide molecule when such fragments or precursors show the same activity of the protein of the invention, as medicament.
The definition xe2x80x9cfusion proteinxe2x80x9d as herein used refers to polypeptides comprising the polypeptide of the invention above specified fused with another protein and having a longer lasting half-life in body fluids. It can for example be fused with another protein such as, for example, an immunoglobulin.
Another object of the invention is the DNA molecule comprising the DNA sequence coding for the allelic variant of the invention, including nucleotide sequences substantially the same.
xe2x80x9cNucleotide sequences substantially the samexe2x80x9d includes all other nucleic acid sequences which, by virtue of the degeneracy of the genetic code, also code for the given amino acid sequences. In particular, the present invention refers to the nucleotide sequence comprising the SEQ ID NO:1.
The present invention also refers to recombinant DNA molecules which hybridize with the DNA sequence coding for the above-mentioned allelic variant of hSTAT3 and whose nucleotide sequences show at least the same 13 differences in the SH2 domain (with respect to the human STAT3 sequence in Akira et al., 1994), as shown in FIG. 1. The gene can contain, or not, the natural introns and can be obtained for example by extraction from appropriate cells and purification with known methods.
Furthermore, the present invention also includes recombinant DNA molecules which hybridize under stringent conditions with a probe having a nucleotide sequence selected between SEQ ID NO:16 and SEQ ID NO:17.
The term xe2x80x9cstringent conditionsxe2x80x9d refers to hybridization and subsequent washing conditions which those of ordinary skill in the art conventionally refer to as xe2x80x9cstringentxe2x80x9d. See Ausubel et al., Current Protocols in Molecular Biologic supra. Interscience. N.Y. pare. 6.3 and 6.4 (1987, 1992), and Sambrook et al, 1989. Without limitation, examples of stringent conditions include washing conditions 12-20xc2x0 C. below the calculated Tm of the hybrid under study in, e.g. 2xc3x97SSC and 0.5% SDS for 5 minutes, 2xc3x97SSC and 0.1% SDS for 15 minutes; 0.1xc3x97SSC and 0.5% SDS at 37xc2x0 C. for 30-60 minutes and then a 0.1xc3x97SSC and 0.5% SDS at 68xc2x0 C. for 30-60 minutes. Those of ordinary skill in this art understand that stringency conditions also depend on the length of the DNA sequences, oligonucleotide probes (such as 10-40 bases) or mixed oligonucleotide probes. If mixed probes are used, it is preferable to use tetramethyl ammonium chloride (TMAC) instead of SSC. See Ausubel. supra.
The invention also includes expression vectors which comprise the above DNAs, host-cells transformed with such vectors and a process of preparation of such allelic variant of hSTAT3, its active fragments or fusion proteins, through the culture in appropriate culture media of said transformed cells.
The DNA sequence coding for the protein of the invention can be inserted and ligated into a suitable plasmid. Once formed, the expression vector is introduced into a suitable host cell, which then expresses the vector(s) to yield the desired protein.
Expression of any of the recombinant proteins of the invention as mentioned herein can be effected in eukaryotic cells (e.g. yeasts, insect or mammalian cells) or prokaryotic cells, using the appropriate expression vectors. Any method known in the art can be employed.
For example the DNA molecules coding for the proteins obtained by any of the above methods are inserted into appropriately constructed expression vectors by techniques well known in the art (see Sambrook et al, 1989). Double stranded cDNA is linked to plasmid vectors by homopolymeric tailing or by restriction linking involving the use of synthetic DNA linkers or blunt-ended ligation techniques: DNA ligases are used to ligate the DNA molecules and undesirable joining is avoided by treatment with alkaline phosphatase.
In order to be capable of expressing the desired protein, an expression vector should comprise also specific nucleotide sequences containing transcriptional and translational regulatory information linked to the DNA coding the desired protein in such a way as to permit gene expression and production of the protein. First in order for the gene to be transcribed, it must be preceded by a promoter recognizable by RNA polymerase, to which the polymerase binds and thus initiates the transcription process. There are a variety of such promoters in use, which work with different efficiencies (strong and weak promoters).
For eukaryotic hosts, different transcriptional and translational regulatory sequences may be employed, depending on the nature of the host. They may be derived form viral sources, such as adenovirus, bovine papilloma virus, Simian virus or the like, where the regulatory signals are associated with a particular gene which has a high level of expression. Examples are the TK promoter of the Herpes virus, the SV40 early promoter, the yeast gal4 gene promoter, etc. Transcriptional initiation regulatory signals may be selected which allow for repression and activation, so that expression of the genes can be modulated.
The DNA molecule comprising the nucleotide sequence coding for the protein of the invention is inserted into vector(s), having the operably linked transcriptional and translational regulatory signals, which is capable of integrating the desired gene sequences into the host cell.
The cells which have been stably transformed by the introduced DNA can be selected by also introducing one or more markers which allow for selection of host cells which contain the expression vector. The marker may also provide for phototrophy to a auxotropic host, biocide resistance, e.g. antibiotics, or heavy metals such as copper, or the like. The selectable marker gene can either be directly linked to the DNA gene sequences to be expressed, or introduced into the same cell by co-transfection. Additional elements may also be needed for optimal synthesis of proteins of the invention.
Factors of importance in selecting a particular plasmid or viral vector include: the ease with which recipient cells, that contain the vector may be recognized and selected form those recipient cells which do not contain the vector; the number of copies of the vector which are desired in a particular host; and whether it is desirable to be able to xe2x80x9cshuttlexe2x80x9d the vector between host cells of different species.
Once the vector(s) or DNA sequence containing the construct(s) has been prepared for expression the DNA construct(s) mat be introduced into an appropriate host cell by any of a variety of suitable means: transformation, transfection, conjugation, protoplast fusion, electroporation, calcium phosphate-precipitation, direct microinjection, etc.
Host cells may be either prokaryotic or eukaryotic. Preferred are eukaryotic hosts, e.g. mammalian cells, such as human, monkey, mouse, and Chinese hamster ovary (CHO) cells, because they provide post-translational modifications to protein molecules, including correct folding or glycosylation at correct sites. Also yeast cells can carry out post-translational peptide modifications including glycosylation. A number of recombinant DNA strategies exist which utilize strong promoter sequences and high copy number of plasmids which can be utilized for production of the desired proteins in yeast. Yeast recognizes leader sequences on cloned mammalian gene products and secretes peptides bearing leader sequences (i.e., pre-peptides).
After the introduction of the vector(s), the host cells are grown in a selective medium, which selects for the growth of vector-containing cells. Expression of the cloned gene sequence(s) results in the production of the desired proteins.
Purification of the recombinant proteins is carried out by any one of the methods known for this purpose, i.e. any conventional procedure involving extraction, precipitation, chromatography, electrophoresis, or the like. A further purification procedure that may be used in preference for purifying the protein of the invention is affinity chromatography using monoclonal antibodies which bind the target protein and which are produced and immobilized on a gel matrix contained within a column. Impure preparations containing the recombinant protein are passed through the column. The protein will be bound to the column by the specific antibody while the impurities will pass through. After washing, the protein is eluted from the gel by a change in pH or ionic strength.
As already stated, the protein of the invention is useful in the therapy and/or diagnosis of autoimmune and/or inflammatory diseases. Therefore, in a further aspect, the present invention provides the use of the protein of the invention in the manufacture of a medicament for the treatment of autoimmune diseases and/or inflammatory diseases.
The medicament is preferably presented in the form of a pharmaceutical composition comprising the protein of the invention together with one or more pharmaceutically acceptable carriers and/or excipients. Such pharmaceutical compositions form yet a further aspect of the present invention.
The invention will now be described by means of the following Examples, which should not be construed as in any way limiting the present invention. The Examples will refer to the Figures specified here below.